wasmtime is a fast and secure runtime for WebAssembly. Wasmtime's code generation backend, Cranelift, has a bug on x86_64 platforms for the WebAssembly `i8x16.select` instruction which will produce the wrong results when the same operand is provided to the instruction and some of the selected indices are greater than 16. There is an off-by-one error in the calculation of the mask to the `pshufb` instruction which causes incorrect results to be returned if lanes are selected from the second vector. This codegen bug has been fixed in Wasmtiem 6.0.1, 5.0.1, and 4.0.1. Users are recommended to upgrade to these updated versions. If upgrading is not an option for you at this time, you can avoid this miscompilation by disabling the Wasm simd proposal. Additionally the bug is only present on x86_64 hosts. Other platforms such as AArch64 and s390x are not affected.

wasmtime is a fast and secure runtime for WebAssembly. In affected versions wasmtime's code generator, Cranelift, has a bug on x86_64 targets where address-mode computation mistakenly would calculate a 35-bit effective address instead of WebAssembly's defined 33-bit effective address. This bug means that, with default codegen settings, a wasm-controlled load/store operation could read/write addresses up to 35 bits away from the base of linear memory. Due to this bug, however, addresses up to `0xffffffff * 8 + 0x7ffffffc = 36507222004 = ~34G` bytes away from the base of linear memory are possible from guest code. This means that the virtual memory 6G away from the base of linear memory up to ~34G away can be read/written by a malicious module. A guest module can, without the knowledge of the embedder, read/write memory in this region. The memory may belong to other WebAssembly instances when using the pooling allocator, for example. Affected embedders are recommended to analyze preexis…